Method of and apparatus for inspecting liquid storage tanks for leaks by means of pressure decrease and increase

ABSTRACT

A method of inspecting storage tanks for leaks by means of pressure decrease and increase in the tanks, in which a part of a liquid 6 stored in a tank 1 is discharged to put the tank 1 under vacuum and variations in the pressure in the tank 1 with time are checked, the pressure in the tank 1 is thereafter increased to the level of the atmospheric pressure, and then the liquid which was discharged from the tank is poured back thereinto to put the tank under pressure and variations in the pressure in the tank with time are checked. The method is done by an apparatus designed for inspecting storage tanks for leaks by means of pressure decrease and increase in the tanks, having an air pipe (2), a measuring pipe (3), a liquid feed pipe (4), a liquid suction pipe (5) and an air-tight container (7), which are communicated with a tank (1) to be inspected, a pressure regulator pump (8) connected to the air-tight container (7), and a manometer (11) and a recording air gauge (10) connected to the measuring pipe (3).

DESCRIPTION

1. Technical Field

This invention relates to a method of and an apparatus for inspectingliquid storage tanks for leaks.

2. Background Art

In a method generally used of inspecting tanks for leaks, the tank isentirely emptied, the pressure in the tank is increased or decreased,and pressure variations with time are checked while the tank is underpressure or vacuum to determine whether the tank has a leak. However, ittakes a lot of time and money to empty the tank, and this step can bevery dangerous when the tank contains certain kinds of liquids. Moreoverit takes much more time to make preparations for the inspection and forprocedures afterwards than to actually inspect the tank. This causes agreat loss of time.

DISCLOSURE OF INVENTION

The present invention provides a method and an apparatus whicheliminates these drawbacks, and makes it possible to inspect a storagetank safely and reliably with the liquid left therein.

The inspection method according to the present invention ischaracterized in that it comprises the steps of air-tightly closing atank with a liquid stored therein, discharging a part of the liquid fromthe tank to put the tank under vacuum and checking variations in thepressure therein with time; raising the pressure in the tank back toatmospheric pressure and then putting the tank under pressure by pouringthe liquid discharged from the tank in the preceding discharging stepback into the tank, and checking variations in the pressure in the tankwith time.

The inspection apparatus according to the present inventioncharacteristically comprises an air pipe, a measuring pipe and a liquidfeed pipe, which are communicated with upper portions of a tank to beinspected, a liquid suction pipe communicated with a lower portion thetank to be inspected, an air-tight container communicated with a lowerportion of the tank to be inspected via a valve, a pressure regulatorpump communicated with the air-tight container, a manometer and arecording air gauge which are joined to the measuring pipe, and a valveconnected to the measuring pipe and adapted to open the interior of themeasuring pipe to atmospheric pressure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of a method of inspecting storage tanksfor leaks by means of pressure decrease and increase according to thepresent invention; and

FIGS. 2 and 3 show examples of inspection curves obtained in the method.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to the drawings.

Referring to FIG. 1, reference numeral 1 denotes a tank to be inspected,2 an air pipe communicated with the tank 1 at an upper portion thereof,3 a measuring pipe communicated with the tank 1 at an upper portionthereof, 4 a liquid feed pipe also communicated with the tank 1 at anupper portion thereof, 5 a suction pipe communicated with the tank at alower portion thereof, and 6 a liquid stored in the tank 1.

According to the present invention, a small air-tight container 7 isprovided with a pressure regulator pump 8 connected to an upper portionthereof, the suction pipe 5 which is communicated with the tank 1 beingconnected to a lower opening of the container 7 via a valve 9. One endof a manometer 11 and a recording air gauge 10 are joined to, forexample, the measuring pipe 3 communicated with an upper portion of thetank 1. The other end of the manometer 11 is left open to atmosphericpressure. Blind covers are then put on the air pipe 2 and liquid feedpipe 4 to make the interior of the tank air-tight. The pressureregulator pump 8 is actuated to put the small air-tight container 7under vacuum. The valve 9 is opened to apply the vacuum to the suctionpipe 5 to suck up some of the liquid 6 stored in the tank into the smallair-tight container 7 to store it therein. When a device for extractingthe liquid in storage, such as a pump, is connected to the tank 1 theliquid may be sucked up in the depressurizing step. A chain line in thetank 1 represents the level of the liquid before any of it was suckedup.

The valve 9 is closed with the pressure in the space in the tank 1 thusreduced. At this time, the difference H between the pressure in the tank1 and the atmospheric pressure, which difference H varies according tothe pressure in the tank, is indicated by the manometer 11.

If the tank 1 has a leak, air enters the tank 1 from the outside sinceits interior is under vacuum. Consequently, the pressure in the tank 1increases with time, and the water column difference H in the manometeris decreased.

The existence of a leak in the tank can be determined generally withreference to only the amount of the decrease in the water columndifference H in the manometer 11. However, when certain kinds of liquidare stored in the tank, the pressure increases from the influence of thevapor pressure of the liquid even if no leaks exist in the tank, leadingthe inspector to believe that a leak exists in the tank. Variations inthe pressure in the tank due to the vapor pressure of the liquid instorage will be described briefly with reference to the graph in FIG. 2.

Referring to FIG. 2, a curve l₁ denotes the relation between thepressure in the tank and the lapse of time when the liquid in storagehas a comparatively low vapor pressure, such as water or kerosene. Thecurve l₁ shows that, when no leak exists, the pressure does not varywith time. When a leak exists, the pressure returns to atmosphericpressure in a short period of time as shown in a curve l₃, but does notexceed atmospheric pressure. When a liquid having a high vapor pressuresuch as a volatile oil is stored in the tank, the pressure increaseswith time, as shown by curve l₂, due to the pressure increase from thevapor pressure of the liquid even if no leak exists. This leads theinspector to believe that a leak exists in the tank. However, when atank containing a liquid having a high vapor pressure is inspected, theinfluence of the vapor pressure can be eliminated by continuouslycarrying out a step which will be described later.

After the above-mentioned steps have been carried out, for example, thevalve 12 connected to the measuring pipe 3 is opened to allow thepressure in the tank 1 to return to atmospheric pressure, and thereafterclosed to make the tank 1 air-tight again. The pressure regulator pump 8is then set and actuated to put the small air-tight container 7 underpressure. The valve 9 is opened to allow the liquid 6 stored in thecontainer 7 to be poured back into the tank 1 via the suction pipe 5.Thus, the liquid sucked up in the preceding step is returned to the tank1 to raise the level in the tank up to the chain line. In this storedliquid returning step, the liquid may be sent back to the tank 1 bygravity only, without increasing the pressure in the small air-tightcontainer 7. The space in the tank 1 is thus put under pressure inaccordance with the increase in the liquid level, and the manometer 11indicates the difference h between the pressure in the tank 1 and theatmospheric pressure, in accordance with the condition of the pressurein the tank 1, Variations in the pressure in the tank 1 are recorded atpredetermined time intervals as shown in FIG. 3, and whether or not aleak exists can be determined even when the vapor pressure of the liquidin the tank 1 is high, after the records of both vacuum and pressurizedstages have been discussed collectively.

Referring to FIG. 3, the region between points a and c records thevacuum stage, and that between points d and e records the pressurizedstage. The data between points a and b and between points d and e arethose in initial unstable periods, and are not used to give a decisionin the leakage inspection. Now, let T equal the time during which thepressure in the tank in the vacuum stage varies linearly, P the amountof variation in this pressure, T' the time during which the pressure inthe tank in the pressurized stage varies linearly, and P' the amount ofvariation in the pressure in the latter stage. When no leaks exist inthe tank with a liquid of a low vapor pressure stored therein, thevalues of both P and P' are close to zero. When the vapor pressure ofthe liquid is high and the tank has no leaks, then P/T≈P'/T', and whenthe tank has a leak, P (in the vacuum stage)=pressure increase due tothe leak+vapor pressure, so that P' (in the pressurized stage)=vaporpressure-pressure loss due to the leak; and accordingly, P/T>P'/T'.

As a result, whether or not a leak exists can be determined very easily.

A liquid has a more or less unique vapor pressure, so the method andapparatus according to the present invention can be used effectively toinspect a storage tank with the stored liquid left therein.

Industrial Applicability

As described above, the method of and apparatus for inspecting storagetanks for leaks by means of pressure decrease and increase in the tankare greatly advantageous in that they permit inspection of a tank forleaks extremely safely and reliably irrespective of the kind of theliquid stored therein.

I claim:
 1. A method of testing for leakage of a tank that contains aliquid having a high vapor pressure, said method being characterizedby:A. sealing the tank from the atmosphere; B. with the tank thussealed, withdrawing from the tank to a container a part of the liquidstored in the tank, to reduce pressure in the portion of the tank thatis above the liquid therein to a subatmospheric value; C. making a firstmeasurement of the rate of increase per unit of time of pressure in saidportion of the tank, during at least a final portion of a period longenough to ensure that said rate has attained a stable value; D. whilesaid part of the liquid remains in said container, venting the tank toatmosphere to equalize pressure in said portion of the tank withatmospheric pressure; E. thereafter resealing the tank from theatmosphere; F. with the tank resealed, returning to the tank from saidcontainer the part of the liquid that had been withdrawn from the tank,to increase the pressure in said portion of the tank to anabove-atmospheric value; and G. making a second measurement of the rateof increase per unit of time of pressure in said portion of the tank,through at least a final portion of a period long enough to ensure thatsaid rate has attained a stable value, for comparison with the ratefound by said first measurement, the existence of a leak in the tankbeing signified by a difference between the compared rates.
 2. Apparatusfor testing for leakage of a tank that contains a liquid having a highvapor pressure, said apparatus comprising:A. means for readily openablysealing the interior of the tank from the atmosphere so that the spacein the tank that is above the level of said liquid therein can beselectably evacuated, vented and pressurized; B. a container for holdinga quantity of said liquid that is substantially less than the amount ofsaid liquid normally in the tank; C. duct means in sealed relation tosaid tank and said container, for communicating the interior of thecontainer with the interior of the tank near the bottom thereof; D. avalve in said duct means that can be alternatively opened forcommunication of the tank and the container and closed for blocking suchcommunication; E. means defining a vacuum source communicable with theinterior of said container to enable a portion of the liquid in the tankto be drawn into the container when the tank is sealed, to produce asubatmospheric pressure in said space; and F. a recording pressure gagecommunicating with said space in the tank, to provide for a firstmeasurement of the rate of increase of pressure in said space after saidsubatmospheric pressure has been produced and for a second measurementof said rate after the tank has been vented to atmosphere and resealedand liquid has then been returned from the container to said tank topressurize said tank, so that leakage can be ascertained from adifference between the rates found in the first and second measurements.